The invention relates to semiconductor packages, the provision of a leadframe and semiconductor packages including the leadframe. The invention also relates to leadless semiconductor packages as well as to methods for producing the leadframe and semiconductor packages.
Existing leadframe-based leaded and leadless packages are known to suffer from various technical problems. The difference in the Coefficient of the Thermal Expansion between the various elements of a typical semiconductor package, such as the semiconductor chip, the leadframe, and the mold compound, and creates warpage and internal stresses within the semiconductor package. This can lead to the formation of cracks and delamination at the interfaces between the different materials. This in turn can lead to failure of the package.
The problem of the difference in thermal expansion coefficients is exacerbated by the large number of interfaces in the package itself. For example, there are interfaces between the semiconductor chip and the mold compound, the semiconductor chip and the glue or die attach material and the glue and the leadframe.
Additionally, heat dissipation from known leadframe-based packages is inefficient, especially for leaded packages, as there is a long path for the dissipation of the heat generated by the semiconductor chip. A further known disadvantage is the antenna effect which is caused by the long electrically conductive path of the package. The electrical path includes the length of the bond wire from the semiconductor chip to the contact pad of the lead of the leadframe and the length of the lead from the inner contact pad to the board on which the package is mounted. The antenna effect is a particular problem for RF application devices.
These problems have been addressed using various approaches. To reduce the mismatch in the Coefficient of Thermal Expansion, the materials used for the package are carefully chosen. Although this approach may reduce the mismatch, the mismatch is not completely eliminated. The costs of the materials used also tend to be higher and this increases the cost of the package.
Thermal dissipation from the package can be improved by providing a package in which the die paddle or die pad is exposed in the outer surface of the package. Alternatively, the use of a die pad is avoided, as is disclosed in U.S. Pat. No. 6,723,585. The problem of the antenna effect has been tackled by controlling the length of the bond wires between the semiconductor chip and the leads of the leadframe. However, the nature of the wire bonding process places a limit on the minimum length of bond wire and a limit on the height of the loop of the bond wire. The improvements possible by this approach are, therefore, limited.